The present invention relates to a continuously variable transmission, at times referred to as a CVT. Transmissions of this type are well known in the art, and comprise a pair of cone pulleys, each pulley having a pair of sheaves or flanges. The pulleys are interconnected by a belt or the like. In the usual CVT, one pulley is connected to a drive or input shaft and the other pulley is connected to a driven or output shaft. Usually one flange of each pulley is axially movable on its respective shaft with respect to the other flange. By varying the spacing between the flanges of each pulley, continuous adjustment of the drive ratio is provided between the shafts within the limits of pulley sizes. Mechanical or hydraulic means and/or combinations of the two means are usually provided for initiating the drive ratio changes. The prior art is replete with such arrangements.
The axially movable flange of each pulley or a hub of such flange may be, according to the prior art, provided with an internal keyway to receive a key fitting in a keyway in the respective shaft to provide the driving connection between flange and shaft while permitting axial movement of at least one of the flanges. The keyways are machined in the shafts and flanges, an expensive procedure, and lubrication of the key-keyway connection is difficult at times. In the absence of proper lubrication, the key bends in the keyways and the movable flange behaves as a fixed flange, so that drive ratio changes are impeded. Loading on the key, under these circumstances, becomes excessive because of the physical mass of the pulley rotating at relatively high speeds and leads to premature failure of the transmission.
Another form of movable flange-shaft connection is the ball-spline in which a plurality of balls are used with a spline, the balls functioning as anti-friction elements. The ball-spline connection is located internally of the flange and/or its hub. This type of connection is expensive and requires continuous lubrication to insure continued performance. Loading on the spline of the ball-spline connection can also become excessive, leading to premature failure of the transmission.
Instead of the movable flange-shaft connections, as above described, Bessette, in U.S. Pat. No. 3,868,862, teaches the use of a pivotably connected link or links between the movable flange and the drive member. In one embodiment a single link is generally circumferentially arranged with respect to the flange and drive member, and in another embodiment, three spaced links are angularly arranged with respect to the flange and drive member. In both embodiments, the links must be rigid or stiff and must be provided with pivoting joints which, in the case of the second embodiment, are universal joints. To operate properly, these joints must be constantly lubricated. The link or links exert a force component to the pulley flange which either adds to or subtracts from the force applied by other means to the flange.